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Freelite assays are latex-enhanced immunoassays that utilise sheep polyclonal antisera. They are the only FLC assays that are recommended by name in International Myeloma Working Group (IMWG) guidelines (Sections 8.7 and 25.3). By contrast, each of the other commercial FLC assays has features that may limit their usefulness. Trimero Diagnostics manufactures latex-enhanced immunoassays that are intended for use with serum and urine. However, to our knowledge, there are no peer-reviewed publications containing data of their assay's performance. There are also no publications on the use of the Diazyme human FLC assay, which only has regulatory approval for one turbidimetric instrument and has a very limited intended use. The Biovendor FLC assays are enzyme-linked immunosorbent assays (ELISAs). Whilst this assay format can achieve high sensitivity, they are intended for research use only. Sebia FLC assays are also based on an ELISA format, and are reported to produce results that are more coherent with those obtained by serum protein electrophoresis (SPE). However, use of SPE as the gold standard for light chain quantitation is debatable (Section 4.2.3).

Two commercial FLC assays intended for routine clinical use are based on monoclonal antibodies: Abingdon Health manufacture Seralite-FLC lateral flow FLC immunoassays [920] and Siemens supply N Latex FLC nephelometric FLC immunoassays[199]. A number of studies have concluded that values returned by monoclonal antibody-based FLC assays do not compare well with those returned by the polyclonal antibody-based Freelite assays. Of most concern is the fact that monoclonal antibody-based assays may fail to recognise a particular tumour-derived FLC clone, which can be detected by the Freelite assays. These and other issues are further discussed below.